Michael,
Sound reproduction systems are, to a high degree, up to personal taste and preferences, what sounds excellent to one may sound mediocre to another. Also, there is matter of integration between components, especially between pre-amp, power amp (or integrated amp) and speakers.

Many tube amps are colored, however, those designs which sound clean and neutral are really excellent – to my taste and preferences. Most SS amps I heard are "analytical", "lifeless" "not musical". That being said, right now my phono stage and pre-amp are tubes and the power amp is SS – and my setup sounds to me excellent. However, the amps I use at the moment are not the final word and I intend to give a try to some others. I have a tube power amp which sounded great with my previous speakers but exaggerates low frequencies with my present speakers. So, to a high degree it's a matter of integration.

Well said, Joshua. Even though I have never made a commercial tube design, I was taught tube design in college (yes, I am that old), and used tubes primarily for my first 10 years in hi fi, and for 5 years before that even, with a 1938 Gibson tube amp (pp6L6) open loop, and an electrodynamic magnetic coil speaker. (what comes around, goes around). I have listened to McIntosh, Marantz, Dyna, and Fisher for decades. Still do, sometimes, yet I just don't have that much to contribute to tube design. I like complementary circuits, because I can think 'upside down' unlike some friends of mine. ;-) Only solid state gives me that advantage.

It must be pointed out that single ended is ALWAYS Class A, Complementary design gives you a choice to bias Class A , Class AB, or even Class B. Class A is always best, but you do get more power from Class AB or Class B.
All my discrete preamps are Class A throughout. My power amps are Class A up to the output stage, which is usually Class AB, in order to get more power from a given heat sink.

As you know, gm of jfet and mosfet tends to be arise from higher current, meawhile gm of bipolar tends to be as contrary to higher current.

Francesco.

No, Fet's go roughly as the square root of current and bipolars are directly proportional to current. There are limits, but not of interest for small signal amplifiers.

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"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."